The emergence of the Acquired Immunodeficiency Disease (AIDS) pandemic may represent the most serious global public health threat of the 20th century. The goal of the proposed research is the development of an efficacious vaccine against multiple strains of the Human Immunodeficiency Virus (HIV), the etiological agent of AIDS. This proposal describes the design, construction and evaluation of a series of vaccinia-based recombinant vaccines for both HIV-1 and the related Simian Immunodeficiency Virus (SIV). This will be accomplished through a coordinated program combining the talents of both academic and industrial scientists. These vaccines will express multiple HIV-1 or SIV antigens in conformations that elicit appropriate humoral and cell-mediated immune responses. Novel methods developed at AbT for rapidly generating and selecting vaccinia recombinants expressing multiple antigens are described. The nature and magnitude of the humoral and cell mediated immune responses elicited by the recombinant viruses will be evaluated in both murine and non-human primate systems. In addition, histocompatible human target cells infected with the recombinant viruses will be used to assess, in vitro, cytotoxic cellular responses of HIV-1 infected individuals to the vaccinia-expressed HIV-1 antigens. These in vitro studies will help define the HIV-1/SIV antigens and /or antigenic epitopes most appropriate for inclusion into a potential vaccine. The demonstration of the efficacy of an HIV-1 vaccine is hampered by the lack of the induction of an acquired immunodeficiency syndrome in HIV-1 infected non-human primates. The development of an AIDS- like syndrome in macaques following infection with SIV allows the evaluation of the efficacy of potential vaccines in a primate model. This system will permit characterization of the immune responses induced and the protection afforded by vaccinia recombinants expressing combinations of SIV antigens. The information derived from these combined HIV-1 and SIV studies will be elaborated to produce safe and efficacious vaccinia-based HIV- 1 vaccines for use in humans.